82 replies to this topic

[Diverbrian]

Trace, do you remember what the dive profiles looked like at WKPP pre-RB80?

Clearly, I understand needing large steel cylinders for long exposures, but come on.. why take 130s to do a 45 minute dive at 130ft?

With a working SAC of 0.8 and a resting SAC of 0.5, Air for bottom gas and Nitrox 50 for deco, V-Planner calculates 180 cf of backgas and 38 cf of deco gas. Using rule of thirds tells me I need 270 cf of backgas. Doubled 130s sounds pretty close. Am I missing something here?

I don't do a forty-five minute bottom time at 130 ft. That would be excessive deco in my opinion. I think most cold water divers don't go much above a 30 min. bottom time for a 130 ft. dive. Otherwise all of that deco gets awful cold, even in a drysuit. I think Perrone is talking about forty-five minutes of run time and not bottom time.

[PerroneFord]

Think about this, no diver ever died from having too much breathing gas. Most of the time they died from not having enough breathing gas.

True, but I've seen some die from being too negative...

[PerroneFord]

With a working SAC of 0.8 and a resting SAC of 0.5, Air for bottom gas and Nitrox 50 for deco, V-Planner calculates 180 cf of backgas and 38 cf of deco gas. Using rule of thirds tells me I need 270 cf of backgas. Doubled 130s sounds pretty close. Am I missing something here?

Yea,

You gotta tell me what agency espouses doing deco dives at 130 with air, and what agency says calculate ocean dives on thirds. That's really new to me.

V-Planner says you need 270cuft of gas for a 45 minute dive? Or for a 45 minute bottom time?

[PerroneFord]

I don't do a forty-five minute bottom time at 130 ft. That would be excessive deco in my opinion. I think most cold water divers don't go much above a 30 min. bottom time for a 130 ft. dive. Otherwise all of that deco gets awful cold, even in a drysuit. I think Perrone is talking about forty-five minutes of run time and not bottom time.

Yea, I'm trying to get back on the boat in an hour allowing room for contingencies like having trouble locating the upline, having to shoot a bag, etc.

[6Gill]

I guess what I am seeing is that you guys in the ocean (or with very deep bottoms) are not wearing weightbelts. I think for me, I'd prefer to wear the AL tanks and a small weightbelt. Ditching the belt in the event of a flood would bring me back to neutral or nearly so. And then I could work from there. Here in the springs I am diving wet, AL80 doubles, no can light for now, and don't wear any weigth. If I lost the wing, I could literally crawl out of any of the places I dive. Or shoot a bag.

With a non-reachable bottom below me (either because of depth or MOD) I'd prefer a way to get neutral or positive by ditching weight. If I was wearing 108s, or 130s, or God forbid 104s, I would be in a very difficult position I think.

I do agree that bringing one set of doubles is easier. But I think I'd rather deal with the inconvenience than deal with the potential hazards.

This has been a very informative thread. Thank you all.

I don't wear a weightbelt and if ditching weight was really neccery...bye bye batteries(I'll keep the lighthead)
I agree if you are wearing 104s/130s in a wetsuit would not be a good idea.I dive a drysuit,I don't have to deal with suit compression at depth.Even if the suit floods there is so little air in there that I wouldn't lose much lift.Even in warmer water for longer dives requiring these tanks I'd be in a drysuitFor me any diving I do up here switching to AL80 would mean having to add ballest so either way I've still got the weight which I feel is more useful as gas/steel tanks then lead.
Not sure you mean by potental hazzards?
We dive some pretty isolated areas so space can be a premium 'cause our choices in boats are limited.I'm doing with one set of doubbles what will take you 3 AL80s in less space.

[6Gill]

You're disappointing the dive centers who are told to encourage prospective open water students to "start today" with technical training.

What? You've seen the new banner at our shop???

Please tell me that was a joke!

~ Trace

She left out the the part about the two arrows(one at each end of the banner)Left side says pay here,right side says pick up card here as soon as payment clears

[6Gill]

Clearly, I understand needing large steel cylinders for long exposures, but come on.. why take 130s to do a 45 minute dive at 130ft?

I can't afford to own all the tank sizes so I have to pick and choose to what gives me the most bang for my bucks.
If you need less gas then the twin 80s gives you but more than a single 80 does and you own both set ups do you go out and buy a tank set up or make do with the twins?

[6Gill]

True, but I've seen some die from being too negative...

Absolutly...but the cases I've seen is a combination of factors...starting with the weightbelt.
It is my opinion that what is required by most training bodies that instuctors spend explaining,teaching and properly demontrating proper weighting to students is inadaquate.As in anything there are those that go above and beyond but they are the exception.Proper weighting takes time and involves more than handing weights to a student till they sink.As an example,my dive buddy got new drysuit underware(type and brand) we then did a shallow dive experimenting to get the weight close and then there was another 4 dives that involved fine tuning(amount and placement of weight)before he was ready to say it was dialed in.
As was pointed out in the pre-BCD days more time and effort was spent fine tuning weights.BCds have allowed people to be sloopy...
I just want to add that this has been a great disscusion....

[Geek]

With a working SAC of 0.8 and a resting SAC of 0.5, Air for bottom gas and Nitrox 50 for deco, V-Planner calculates 180 cf of backgas and 38 cf of deco gas. Using rule of thirds tells me I need 270 cf of backgas. Doubled 130s sounds pretty close. Am I missing something here?

Yea,

You gotta tell me what agency espouses doing deco dives at 130 with air, and what agency says calculate ocean dives on thirds. That's really new to me.

V-Planner says you need 270cuft of gas for a 45 minute dive? Or for a 45 minute bottom time?

No. V-Planner says you need about 180 cf. Rule of thirds takes you to 270 cf. Any deco dive is considered an overhead dive, and if you are spending 45 minutes on a wreck then you may be doing penetration. That is two overhead factors. Are you saying you would not use thirds? What rule are you using for contingencies? Even without the contingency gas you aren't going to do this on the 150 cf you have in AL80s.

You also seem to be thinking that a NE wreck dive is like a FL reef dive. It isn't. Stuff happens.

Whether you use air or some other mix doesn't change your SAC rate. You're going to need 180 cf of something, plus deco gas. I used Nitrox 50 for the deco gas in this calculation, and I am not counting 38.5 cf of that. I am just looking at the back gas.

[Diverbrian]

With a working SAC of 0.8 and a resting SAC of 0.5, Air for bottom gas and Nitrox 50 for deco, V-Planner calculates 180 cf of backgas and 38 cf of deco gas. Using rule of thirds tells me I need 270 cf of backgas. Doubled 130s sounds pretty close. Am I missing something here?

Yea,

You gotta tell me what agency espouses doing deco dives at 130 with air, and what agency says calculate ocean dives on thirds. That's really new to me.

V-Planner says you need 270cuft of gas for a 45 minute dive? Or for a 45 minute bottom time?

IANTD Adv. Nitrox teaches light deco at 130 on air (or EAN28). I actually prefer a little helium in the mix to take the edge off of the narcosis after 100 ft., but not as much as some agencies advocate. And Geek is correct, the minute that you enter deco, you are entering into an overhead environment. Hence, you are looking at rule of thirds.

As I said, I get the impression that we are comparing apples to oranges. A forty-five minute bottom time at 130 ft. is a far cry from a forty-five minute run time. A forty minute bottom time with EAN28 using IANTD tables indicates four deco stops totalling 31 minutes of deco on EAN50. Add another eight to the shallow stops if you are forced to do the whole dive on EAN28. Sounds like a lot a of getting cold to me . PS No deco time on that table is 12 minutes of bottom time. I don't like short dives like that either .

As to some of the other comments, ditching a canister light doesn't help me. I have the small NiMH batteries which mean it doesn't add much weight. Ditching a stage might except that I want that gas on the way up to deco off of. As all of my tanks empty out (I have run that experiment with my deco obligation killed off), I have been known to find myself almost positive with a drysuit and undies. Yes, the catch is (and I am not about to intentionally flood my suit and soak my drysuit undergarments) if those undergarments become saturated with water and all of the air spaces that they had when I decended went away. I have not heard of a diver not being able to make it to the surface this for this reason. That's why they make fins and eventually lift bags . Also, the odds of having a BC rip wide open on the same dive as a drysuit are relatively low. Fifty-five pounds of lift is much more than people would think. I have brought up a thirty some-thing pound weight belt that a student dropped and had enough to get to the surface with that wing (Yes, that was with doubles and I should have used a lift bag. I did on the weight belt that we found at 125 ft. the next day.).

You will generally go through a lot more breathing gas in cold water than you do in warm water. The double eighties leave a marginal amount of gas. Now, what about your buddy if they need gas and you are both stressed? Stuff happens. I can get out of it as a survivor if I can think. I may not necessarily think well if I know that I am running the dive up the edge of my gas supply. The extra gas gives me that room for that "what if" factor as well.

[PerroneFord]

No. V-Planner says you need about 180 cf. Rule of thirds takes you to 270 cf. Any deco dive is considered an overhead dive, and if you are spending 45 minutes on a wreck then you may be doing penetration. That is two overhead factors. Are you saying you would not use thirds? What rule are you using for contingencies? Even without the contingency gas you aren't going to do this on the 150 cf you have in AL80s.

You also seem to be thinking that a NE wreck dive is like a FL reef dive. It isn't. Stuff happens.

Whether you use air or some other mix doesn't change your SAC rate. You're going to need 180 cf of something, plus deco gas. I used Nitrox 50 for the deco gas in this calculation, and I am not counting 38.5 cf of that. I am just looking at the back gas.

Yes, any deco dive is considered an overhead dive. I spend half my time right now doing overhead dives. However, with no swimming exit to contend with, I am MORE than comfortable diving on halfs. If I am doing cave, I will be diving thirds plus rockbottom. Ocean diving, is halves plus rockbottom for my comfort. The idea of thirds was to deal with a swimming exit. Again, I ask what agency is teaching rule of thirds for open ocean dives? If you are doing a wreck penetration, I'd certainly use thirds. Actually, I'd use thirds plus a reserve. And yes, I'd certaly be looking at large tanks.

What makes you think I believe NE Wreck diving is like FL Reef diving? Heck, I've never seen a reef. I have seen some wrecks though. And a number of caverns.

This has probably veered far enough away from lift capacity.

I'll summarize my thoughts:

1. Try to dive with a balanced setup. Meaning that should you lose your primary buoyancy, you won't be in a horribly negative scenario.

2. That means you are going to have to either dive with tanks that make you neutral, carry backup buoyancy, or use a weightbelt. Or some combination of the above.

3. In my estimation, if you are doing technical diving, you should be willing to purchase the right tool for the job at hand. If the dive calls for you carry 300cuft of gas, then don't dive AL80s and a bunch of stages. If the dive calls for 100cuft of gas, don't carry twin 121s.

4. It's interesting that it breaks down nicely. For longer and deeper dives, you are going to get cold if you don't wear better exposure protection. This requires more weight, and thus larger tanks. Which keeps you balanced. Short and shallow dives often don't need heavy exposure gear nor do they require heavy tanks. So again, the rig stays balanced. For the work I am doing 75-120ft in warm water, my AL80s are lovely. I will add a set of 108s for cave work, and a set of 130s for longer cave work or deeper ocean work. I will avoid 104s simply because they are heavier than anything I forsee needing unless I start taking regular trips to the great lakes.

5. In none of these cases I've mentioned, can I see needing more than 60# of lift, and in most cases, probably half that. The gas swing on a set of 130s is probably 12 pounds, less with helium. If the rig is balanced, that should be all you have to lift with your BC. If you have to deal with a flooded suit, or a buddy's failure, you'd have PLENTY of reserve left with a 45# lift wing.

6. I find it somewhat scary when I hear drysuit divers saying they need 30+ pounds of lead. To me, that indicates they are using the wrong BC, or the wrong tanks or both. I'm talking doubles divers here, not single tank divers. If the diver found themselves in a position to have to drop the belt, there is simply no way they could control the ascent. I'd really not want more than 10 pounds on a weightbelt under most circumstances.


Thank you all, this discussion has been very helpful in understanding many things.

[peterbj7]

6. I find it somewhat scary when I hear drysuit divers saying they need 30+ pounds of lead. To me, that indicates they are using the wrong BC, or the wrong tanks or both. I'm talking doubles divers here, not single tank divers. If the diver found themselves in a position to have to drop the belt, there is simply no way they could control the ascent. I'd really not want more than 10 pounds on a weightbelt under most circumstances.

Such a situation can easily arise. My UK O/C setup is twin 12ltr steels with one or two steel side slings of 7ltr each. Plus all the other junk one dives with. My preference is to use a DR TP with Superwing, and I'll be using my O'Three crushed neoprene suit with heavy Thinsulate inner. With that lot on a sea dive I'm likely to carry between 8 and 12 kilos of lead, and if I run all the tanks well down I'll need it. In very cold water I'll take the lot so I can have a decent amount of air in my suit for deco.

I carry my lead in at least three places, two integrated pouches and one weight harness (the sort that goes over the shoulders - more comfortable and safer than a belt). In the unlikely event (it hasn't happened to me yet) that I have to dump some weight I'll do it a bit at a time, starting with one weight pocket so as not to unbalance me too much.

I don't see an acceptable alternative. Sure, I can transfer some weight from lead to a steel backplate, but I won't because I'm not fond of backplates and that weight then becomes undumpable. Or I can wear a less bulky suit with less air, but I'm very fond of that suit when there are sharp edges around, and I want the air to stay warm. I'm already using steel tanks - what other adjustments can I make?

[PerroneFord]

Tanks perhaps?

But you are thinking this through. If you've got ditchable in manageable chunks, then no problems. It's people who have ALL their ditchable weight on a weightbelt that give me pause. I can't imagine taking 30 pounds of weight off at once.

Sometimes wearing large steel tanks is the right choice. Cave divers do it all the time.

I do wonder how much gas you are diving with in your suit such that you are wearing steel backgas, and steel stages/deco bottles and you still need 8-12 kilos of lead. Are these 232bar tanks or 300bar?

[Geek]

With a working SAC of 0.8 and a resting SAC of 0.5, Air for bottom gas and Nitrox 50 for deco, V-Planner calculates 180 cf of backgas and 38 cf of deco gas. Using rule of thirds tells me I need 270 cf of backgas. Doubled 130s sounds pretty close. Am I missing something here?

Yea,

You gotta tell me what agency espouses doing deco dives at 130 with air, and what agency says calculate ocean dives on thirds. That's really new to me.

V-Planner says you need 270cuft of gas for a 45 minute dive? Or for a 45 minute bottom time?

IANTD Adv. Nitrox teaches light deco at 130 on air (or EAN28). I actually prefer a little helium in the mix to take the edge off of the narcosis after 100 ft., but not as much as some agencies advocate. And Geek is correct, the minute that you enter deco, you are entering into an overhead environment. Hence, you are looking at rule of thirds.

As I said, I get the impression that we are comparing apples to oranges. A forty-five minute bottom time at 130 ft. is a far cry from a forty-five minute run time. A forty minute bottom time with EAN28 using IANTD tables indicates four deco stops totalling 31 minutes of deco on EAN50. Add another eight to the shallow stops if you are forced to do the whole dive on EAN28. Sounds like a lot a of getting cold to me . PS No deco time on that table is 12 minutes of bottom time. I don't like short dives like that either .

As to some of the other comments, ditching a canister light doesn't help me. I have the small NiMH batteries which mean it doesn't add much weight. Ditching a stage might except that I want that gas on the way up to deco off of. As all of my tanks empty out (I have run that experiment with my deco obligation killed off), I have been known to find myself almost positive with a drysuit and undies. Yes, the catch is (and I am not about to intentionally flood my suit and soak my drysuit undergarments) if those undergarments become saturated with water and all of the air spaces that they had when I decended went away. I have not heard of a diver not being able to make it to the surface this for this reason. That's why they make fins and eventually lift bags . Also, the odds of having a BC rip wide open on the same dive as a drysuit are relatively low. Fifty-five pounds of lift is much more than people would think. I have brought up a thirty some-thing pound weight belt that a student dropped and had enough to get to the surface with that wing (Yes, that was with doubles and I should have used a lift bag. I did on the weight belt that we found at 125 ft. the next day.).

You will generally go through a lot more breathing gas in cold water than you do in warm water. The double eighties leave a marginal amount of gas. Now, what about your buddy if they need gas and you are both stressed? Stuff happens. I can get out of it as a survivor if I can think. I may not necessarily think well if I know that I am running the dive up the edge of my gas supply. The extra gas gives me that room for that "what if" factor as well.

Thank you for the IANTD reference. My impression is that while no agency is pushing air at 130, no one is saying not to do air at 130 either, but I am not an instructor and have not checked it. The PADI deep dive specialty, which is to 130 ft. is done with either air or a light Nitrox mix.

I am not interested in a 12 minute bottom time either, which is why I thought we were talking 45 minutes bottom, not total. As far as agencies teaching thirds for overhead dives, I believe it is common and it is what I learned in my TDI deco class. I hav been practicing it since on any deco dive.

The local diving is wrecks. While I am not into penetration myself, on virtually any boat I get on around here, someone is going to be doing penetrations.

Back to the amount of weight. With double steel 100s, I do not use any lead. With double AL80s, which I have not tested, I believe I would need about 16 lbs with the tanks at 500 psi. With the double steel 100s a 50 lb wing is adequate, but struggles with the flooded suit scenario. I believe this is because you don't really get 50 lbs of lift from a wing advertised as such. At least that is the only way I can reconcile the feel of some of the wings I have tried with what I think should be required.

[Diverbrian]

With a working SAC of 0.8 and a resting SAC of 0.5, Air for bottom gas and Nitrox 50 for deco, V-Planner calculates 180 cf of backgas and 38 cf of deco gas. Using rule of thirds tells me I need 270 cf of backgas. Doubled 130s sounds pretty close. Am I missing something here?

Yea,

You gotta tell me what agency espouses doing deco dives at 130 with air, and what agency says calculate ocean dives on thirds. That's really new to me.

V-Planner says you need 270cuft of gas for a 45 minute dive? Or for a 45 minute bottom time?

IANTD Adv. Nitrox teaches light deco at 130 on air (or EAN28). I actually prefer a little helium in the mix to take the edge off of the narcosis after 100 ft., but not as much as some agencies advocate. And Geek is correct, the minute that you enter deco, you are entering into an overhead environment. Hence, you are looking at rule of thirds.

As I said, I get the impression that we are comparing apples to oranges. A forty-five minute bottom time at 130 ft. is a far cry from a forty-five minute run time. A forty minute bottom time with EAN28 using IANTD tables indicates four deco stops totalling 31 minutes of deco on EAN50. Add another eight to the shallow stops if you are forced to do the whole dive on EAN28. Sounds like a lot a of getting cold to me . PS No deco time on that table is 12 minutes of bottom time. I don't like short dives like that either .

As to some of the other comments, ditching a canister light doesn't help me. I have the small NiMH batteries which mean it doesn't add much weight. Ditching a stage might except that I want that gas on the way up to deco off of. As all of my tanks empty out (I have run that experiment with my deco obligation killed off), I have been known to find myself almost positive with a drysuit and undies. Yes, the catch is (and I am not about to intentionally flood my suit and soak my drysuit undergarments) if those undergarments become saturated with water and all of the air spaces that they had when I decended went away. I have not heard of a diver not being able to make it to the surface this for this reason. That's why they make fins and eventually lift bags . Also, the odds of having a BC rip wide open on the same dive as a drysuit are relatively low. Fifty-five pounds of lift is much more than people would think. I have brought up a thirty some-thing pound weight belt that a student dropped and had enough to get to the surface with that wing (Yes, that was with doubles and I should have used a lift bag. I did on the weight belt that we found at 125 ft. the next day.).

You will generally go through a lot more breathing gas in cold water than you do in warm water. The double eighties leave a marginal amount of gas. Now, what about your buddy if they need gas and you are both stressed? Stuff happens. I can get out of it as a survivor if I can think. I may not necessarily think well if I know that I am running the dive up the edge of my gas supply. The extra gas gives me that room for that "what if" factor as well.

Thank you for the IANTD reference. My impression is that while no agency is pushing air at 130, no one is saying not to do air at 130 either, but I am not an instructor and have not checked it. The PADI deep dive specialty, which is to 130 ft. is done with either air or a light Nitrox mix.

I am not interested in a 12 minute bottom time either, which is why I thought we were talking 45 minutes bottom, not total. As far as agencies teaching thirds for overhead dives, I believe it is common and it is what I learned in my TDI deco class. I hav been practicing it since on any deco dive.

The local diving is wrecks. While I am not into penetration myself, on virtually any boat I get on around here, someone is going to be doing penetrations.

Back to the amount of weight. With double steel 100s, I do not use any lead. With double AL80s, which I have not tested, I believe I would need about 16 lbs with the tanks at 500 psi. With the double steel 100s a 50 lb wing is adequate, but struggles with the flooded suit scenario. I believe this is because you don't really get 50 lbs of lift from a wing advertised as such. At least that is the only way I can reconcile the feel of some of the wings I have tried with what I think should be required.

Actually one agency insists that any dive below 100 ft. should be on trimix. I follow that theory in my personal cold water diving for the most part but don't use as much helium as that agency would recommend. I dove EAN30 in North Carolina down to 120 ft. or so with no issue.

My weighting and yours would be similar. Steel HP100's or my E8-130's (hard to believe but true) do get slightly light on deco hangs until I can get all of that pesky gas to vent out of my suit which doesn't always happen easily with the attached boots trapping a little bit. I would probably use a bit less weight with double 80's but I have never had a reason to try them and find out. I did my Adv. Nitrox with my HP100's and never looked back towards lighter doubles. I bought the E8-130's when I got into Tri-mix dives. The next set of doubles will be far lighter as one will be O2 and the other will be diluent . Those will happen in a couple of years. I also use a six pound steel backplate. I don't do much wreck penetration myself, but if the wreck is worth it, I have been known to do it. Our wrecks have very little corrosion, so you don't tend to get the restrictions as tight as the ocean wrecks that I dove in NC. The zebra mussels will kill your drysuit though. On the deeper dives, you can bet someone on our boats will be penetrating on the days when I don't. Have you considered coming out here and seeing what deep freshwater wrecks look like? I love to show them off.

BTW, I was taught rule of thirds for any deco in my IANTD course as well. I assumed that this was standard across all agencies with any kind of overhead?